External storage devices and basics of file

Ms. K. D. Patil, AP, SCOE,Kopargaon 1
External Storage Devices
Prepared By
Ms. K. D. Patil, AP
Department of Information Technology
Sanjivani College of Engineering, Kopargaon

Storage Devices
● A storage device is used in the computers to store the data.
● The media for storing the information in a computer is
usually divided into main two types
● Primary Memory
● Secondary Memory/Auxiliary Memory
● Provides one of the core functions of the modern
computer.
● The amount of data stored is measured in kilobytes (KB).

Primary Storage
● Also known as main memory.
● Main memory is directly or indirectly connected to the central processing unit via a
memory bus.
● The CPU continuously reads instructions stored there and executes them as
required.
● It is characterized by having faster access, costing more per bits and having
smaller capacity.
● Usually uses semiconductor Technology. A semiconductor chip is a very large
scale integrated (VLSI) of transitors and other electronic computers.
● Example:
– RAM
– ROM
– Cache

RAM
● It is called Random Access Memory because any of the data in RAM can be
accessed just as fast as any of the other data.
● Computers store temporary data in the RAM. These could be operating
instructions, loose bits of data or content from programs that are running.
● The contents of RAM are constantly rewritten as the data is processed.
● When the computer is switched off, all the data is cleared from the RAM.
● This type of memory is called volatile (Chage rapidly) because it only stores the
data while the computer is switched on.
● RAM sticks are found on the motherboard.
● There are two types of RAM:
– DRAM (Dynamic Random Access Memory)
– SRAM (Static Random Access Memory)

RAM
● Static RAM
– Faster
– More expensive
– More power consumption
– does not need to be refreshed
● Dynamic RAM
– Slower
– Less expensive
– Less power consumption
– needs to be refreshed thousands of times per second

ROM
● When a computer is first switched on, it needs to load up the BIOS
(Basic Input/Output System) and basic instructions for the
hardware.
● These are stored in ROM (Read Only Memory).
● This type of memory is calleThisd non-volatile (Can’t change
rapidly) because it retains the data.
● Data stored in ROM remains there even when the computer is
switched off.
● ROM can be found on the motherboard.
● ROM memory cannot be easily or quickly overwritten or modified .

Cache
● Cache is a high-speed access area that can be
either a reserved section of main memory or a
storage device.
● Most computers today come with L3 cache or
L2 cache, while older computers included only
L1 cache.

Secondary Storage/External
Storage Devices
● It is not directly accessible by the CPU.
● Computer usually uses its input/output channels
access secondary storage and transfers the desired
data using intermediate area in primary storage.
● Cost is less, storage capacity is more but access
time is also more.
● Example:
– Hard disk

Types
● There are three main types of storage device:
● Those that store data by magnetizing a special material that coats the
surface of a disk.
Eg. magnetic tape, floppy disk, external hard disk drives
● Those that store data using optical technology to etch the data onto
a plastic-coated metal disk. Laser beams are then passed over the
surface to read the data.
Eg. CD, DVD, Blue-ray, M-Disc
● Flash drives use solid state technology and store data in a similar
way to the BIOS chip.
Eg. Memory card, Memory stick, USB drives

Hard Disk
● The hard disk drive is the main, and usually largest,
data storage device in a computer.
● It can store anywhere from 160 gigabytes to 2
terabytes.
● Hard disk speed is the speed at which content can
be read and written on a hard disk.
● A hard disk unit comes with a set rotation speed
varying from 4500 to 7200 rpm.
● Disk access time is measured in milliseconds.

Floppy Disk
● Floppy disks used to be used a lot, but they are unreliable and
don’t hold very much data, so they are rarely used now.
● They hold 1.44 MB of data, so are only really useful for backing
up or moving small files that don’t contain graphics.
● They are easily damaged, which means that files stored on
them won’t always load.
● As flash memory has become cheaper, many new computers
don’t even have a floppy disk drive

Magnetic Tape
● A magnetically coated strip of plastic
on which data can be encoded.
● Tapes for computers are similar to
tapes used to store music.
● Tape is much less expensive than other storage
mediums but commonly a much slower solution
that is commonly used for backup.

Optical Disc
● Optical disc is any storage media that holds content
in digital format and is read using a laser assembly
is considered optical media.
● The most common types of optical media are
– Blu-ray (BD)
– Compact Disc (CD)
– Digital Versatile Disc (DVD)

CDs and DVDs
● CD and DVD look exactly the same, but DVDs hold much more
data than CDs and need different drives to read them.
● CD-ROMs are read only – you can read data from them but
can’t write more data to them.
● CD-Rs allow you to write data once, but you can’t write over it.
● CD-RWs allow you to write data and then record new data over
it.
● DVD-Rs and RWs follow the same pattern.
● You need special software to write to CDs and DVDs – you
cannot simply copy files to them.

Comparison
CD DVD BD
Capacity 700MB 4.7GB - 17GB 50GB
Wavelength 780nm 650nm 405nm
Read/Write
Speed
1200KB/s 10.5MB/s 36MB/s
Example CD-ROM,
CD-R
CD-RW
DVD-ROM
DVD+R/RW
DVD-R/RW
DVD-RAM
BD-R
BD-RE

Flash Drives
● In recent years, flash memory has become much more popular.
● It holds a lot of data in a very small space. Flash drives are available in sizes such as
256MB, 512MB, 1GB, 5GB, and 16GB and are an easy way to transfer and store
information.
● It doesn’t need special software to use it.
● Most computers will recognize the device as soon as you plug it in.
●
Flash memory sticks connect through USB or FireWire ports.
● Many other devices, like digital cameras and MP3 players, also use flash memory.
● Flash memory cards can hold different types of data so your MP3 player could hold a data
file with your homework on it, for example.
● A small, portable flash memory card that plugs into a computer’s USB port and functions as
a portable hard drive.
●
Memory cards are usually read by connecting the device containing the card to your
computer, or by using a USB card reader.

File
● A file is a collection of records.
● large collections of information stored on devices outside the
computer's internal memory.
● It usually implies that the records are stored in secondary
storage in the computer's external memory, on tapes or disks.
● As a result, the ways in which the file must be organized so that
operations on it can be carried out efficiently are dependent on
the characteristics of the secondary storage devices used to
implement the file.
● The basic operations on a file are to insert and delete records,
process or update records, and search for or retrieve records.

File
● Each file is a sequence of records.
● The data is subdivided into records (e.g., student
information).
● Each record is a sequence of fields. (e.g., name,
GPA).
● One (or more) field is the key field (e.g.,name).
● All files are assigned a name that is used for
identification purposes by the operating system and
the user.

Types of File
● A file stored on a storage device is a sequence of bits that can
be interpreted by an application program as a text file or a
binary file file or a binary file.
● Text Files
– A text file is a file of plain text.
– To store these data types, they must be converted to their character
equivalent formats.
– Some files can only use character data types. Most notable are file
streams (input/output objects in some object-oriented language like
C++) for keyboards, monitors and printers.
– This is why we need special functions to format data that is
input from or output to these devices

Types of File
● Binary Files
– A binary file is a collection of data stored in
the internal format of the computer.
– Unlike text files, binary files contain data that is
meaningful only if it is properly interpreted by a
program. If the data is textual, one byte is used to
represent one character (in ASCII encoding). But if
the data is numeric, two or more bytes are
considered a data item.

File Operations
● Using a file in a program is a simple three-step
process
● The file must be opened. If the file does not yet
exits, opening it means creating it.
● Information is then saved to the file, read from
the file, or both.
● When the program is finished using the file, the
file must be closed.

File Operations

Opening a File
● File access requires the inclusion of fstream.h
● Before data can be written to or read from a file,
the file must be opened.
ifstream inputFile;
inputFile.open(“customer.txt”);

Default Open Mode
File Type Default Open Mode
ofstream The file is opened for output only. (Information may
be written to the file, but not read from the file.) If
the file does not exist, it is created. If the file
already exists, its contents are deleted (the file is
truncated).
ifstream The file is opened for input only. (Information may
be read from the file, but not written to it.) The
file’s contents will be read from its beginning. If the
file does not exist, the open function fails.

File Mode Flag
File Mode Flag Meaning
ios::app
Append mode. If the file already exists, its
contents are preserved and all output is written to
the end of the file. By default, this flag causes the
file to be created if it does not exist.
ios::ate
If the file already exists, the program goes directly
to the end of it. Output may be written anywhere
in the file.
ios::binary
Binary mode. When a file is opened in binary
mode, information is written to or read from it in
pure binary format. (The default mode is text.)
ios::in
Input mode. Information will be read from the file.
If the file does not exist, it will not be created and
the open function will fail.

File Mode Flag
File Mode Flag Meaning
ios::nocreate
If the file does not already exist, this flag will
cause the open function to fail. (The file will
not be created.)
ios::noreplace
If the file already exists, this flag will cause
the open function to fail. (The existing file will
not be opened.)
ios::out
Output mode. Information will be written to
the file. By default, the file’s contents will be
deleted if it already exists.
ios::trunc
If the file already exists, its contents will be
deleted (truncated). This is the default mode
used by ios::out.

Opening a File and Closing File
●Opening File
fstream dataFile(“names.dat”, ios::in | ios::out);
●Closing File
fstream dataFile;
dataFile.close();

Testing for Open Errors
dataFile.open(“cust.dat”, ios::in);
if (!dataFile)
{
cout << “Error opening file.n”;
}
OR
dataFile.open(“cust.dat”, ios::in);
if (dataFile.fail())
{
cout << “Error opening file.n”;
}

Detecting the End of a File
● The eof() member function reports when the
end of a file has been encountered.
if (inFile.eof())
inFile.close();
● The eof() function returns true
when there is no more information
to be read.

Reading from the file & Writing to
the File
●
Read operation
fstream fin;
fin.read( (char *) &rec, sizeof(student) );
● The read() function takes two arguments.
● &rec : Initial byte of an object stored in file.
● sizeof(student) : size of object represents the total number of bytes to be read from initial byte.
●
Write operation
fstream fout;
fout.write( (char *) &rec, sizeof(student));
● The write() function takes two arguments.
● &rec : Initial byte of an object stored in memory.
● sizeof(student) : size of object represents the total number of bytes to be written from initial
byte.

External storage devices and basics of file

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